Omer W. Blodgett, Sc.D., P.E.

Take the example of a fabricator making presses. The frame of the press consists of a beam made from a rolled wide flange shape with side brackets welded on each side of the beam, at the end. Various plates are welded in place to box in the side brackets and to connect them to the beam. A large hydraulic cylinder is horizontally mounted. In service, the cylinder exerts a high force that the side brackets resist.

Seeking a solution to the problem, the shop supervisor recalled his experience with coverplated beams made of rolled sections, just like the press. In this example, a coverplate added to the top and bottom of the section increased the section properties in the areas of high moment. The coverplates were applied only in the center portion of the beam, where the bending moments were highest.

The moment diagram shows the magnitude of the moment at the termination of the coverplate.

To solve the cracking problem, the cover plates were lengthened, pushing the termination point into a region of lower stress.

Armed with this thought, the supervisor reasoned he had the reverse situation. He only needed to extend the side bracket into an area of lower stress just like what had been done with the coverplates.

Unfortunately, the bending moment along the length of the beam in the press remained constant.

Alternately, the beam section could remain the same (or even be reduced in size) if the side brackets are made continuous for the length of the assembly.

Taking an engineering principle from one industry and applying it to another is the essence of technology transfer. But if the circumstances surrounding the two applications differ significantly, the transfer may be unsuccessful.

After the first units were fabricated and put into service, the welds joining the side brackets to the beam began to crack. Specifically, the cracking occurred at the termination of the fillet weld at the corner where the side bracket met the rolled shape. At this point, there is a significant change in section and stiffness of the assembly.

When the coverplated beams cracked in service, those cracks also occurred at the termination end of the fillet weld.

The concept was sound, and the fix would have worked if lengthening the side plates had put the termination point into a region of lower stress.

Although the supervisor lengthened the side plate, the welds terminated in a region where the stress was the same as before.

The supervisor created another model, with even longer side plates. Although he was sure this would solve the problem, cracking again occurred at the end of the weld, because the weld still terminated in a region of high stress. The error here was the supervisor's failure to see that the principle behind the success of longer cover plates was not applicable to the press.

There are at least two solutions to the problem. First, maintaining the original side bracket sizes, while increasing the section properties of the beam, will result in decreased stress at the point of weld termination.

This scheme results in limited load transfer from the side plate into the beam, eliminating the abrupt change in section.

The shop supervisor deserves credit for attempting to transfer technology from one application to another, but the effort was futile because the moment distribution was not as assumed.

Omer W. Blodgett, Sc.D., P.E., senior design consultant with The Lincoln Electric Co., struck his first arc on his grandfather's welder at the age of ten. He is the author of Design of Welded Structures and Design of Weldments and an internationally recognized expert in the field of weld design. In 1999, Blodgett was named one of the "Top 125 People of the Past 125 Years" by Engineering News Record. Blodgett may be reached at (216) 383-2225.